1. Field of the Invention
The present invention concerns a device for spooling and unspooling a power cable or the like upon relative displacement of two areas connected to each other by the cable or the like, said device comprising:
a support disposed in one of said areas,
a drum mounted to rotate about a first axis relative to the support and adapted to receive the cable or the like,
drive means for rotating the drum about the first axis in a direction to spool the cable or the like and in a direction to unspool the cable or the like by applying traction to the cable between said areas, said drive means comprising an electric drive motor carried by the support and having a rotary output shaft and a kinematic linkage between the drive motor output shaft and the drum so as to associate with the spooling and unspooling directions respective directions of rotation of the drive motor output shaft, and
control means for said drive means comprising means for supplying electrical power to the drive motor.
2. Description of the Prior Art
Devices of this kind are often used, for example, to supply electrical power from a socket outlet with is fixed relative to the ground to a machine travelling over the ground such as a crane or a locomotive with a small operating radius or moving upwards and downwards relative to the ground such as a lift platform, this machine constituting said area carrying the support while the ground, or more precisely the socket outlet fixed relative to the ground, constitutes the other of said areas. Such devices are also used to supply electrical power from a lifting machine such as a crane constituting said area carrying the support to a handling device such as an electromagnet or an electrohydraulic scoop constituting said other area and carried by this machine at a variable relative height by means of a cable or other suspension means. Such devices may also be used to spool or unspool under similar conditions a flexible bundle of optical fibers or a flexible hose conveying pressurized fluid, although these examples are by no means limiting on the invention. Depending on individual circumstances, the cable is spooled on the drum in a spiral or in a helix or in a combination of these two spooling modes.
These devices must adapt, to suit the speed of relative displacement of the two areas, the speed at which the cable or the like is spooled or unspooled onto or from the drum expressed as a linear speed tangential to the drum at a distance from the axis of the latter or first axis which varies continuously during spiral spooling in order to avoid slack or excessive tension in the cable or the like.
To this end a synchronous motor is usually employed and this is coupled to the drum by a kinematic linkage comprising a coupling which allows slip. The motor is energized so that its output shaft rotates only in the direction corresponding to spooling onto the drum, at an angular speed which is always greater than the required angular speed of the drum which is essentially variable and allowing for the transmission ratio of the kinematic linkage; the coupling is calibrated so that whatever resisting torque the cable opposes to being spooled onto the drum, allowing for the permissible tension in the cable and the variable distance from the drum axis or first axis at which this tension is applied to the drum, the latter actually turns in the spooling direction and the cable is actually spooled onto it as the two areas that it connects to each other move closer together; the torque and speed of the motor output shaft and those of the drum are matched by slip occurring in the coupling, which absorbs energy that is usually converted to heat. During unspooling, the cable or the like is unspooled, entraining the drum in the corresponding direction, only because of the traction applied to it as the two areas that it connects to each other move further apart, and the combination of the coupling which allows slip and the motor opposes a resisting torque and absorbs energy which is also usually dissipated as heat.
In this known form devices for spooling and unspooling a power cable or the like are entirely satisfactory provided that the cable length is moderate, that is to say that the variation of the spooling radius on the drum remains limited, and provided that in cases where the cable is at a variable height and hangs freely from the drum (for example, if a spooling and unspooling device is used to supply power to a lift platform or to a load suspended from a lifting machine as mentioned above) the variation in this height is restricted to a limited range.
If the cable to be spooled or unspooled is long, however, and if a significantly varying free length of cable or the like is suspended directly from the drum the known devices are not satisfactory, in particular because it becomes difficult to calibrate the coupling which allows slip so that the tension in the cable or the like remains at all times below a safe threshold, so avoiding all risk of damage, and so that the device is capable of spooling the cable or the like over a large radius of the drum and/or is capable of spooling significantly varying free lengths of the cable or the like hanging directly from the drum.
In this known form the devices for spooling and unspooling a power cable or the like have the drawback that, because of inertia, the high accelerations on relative movement of the two areas that the cable or the like connects to each other and the high speeds of such displacement cause large variations in the tension in the cable or the like, including values that are not permissible.
An object of the invention is to remedy these drawbacks.